The effects of gamma irradiation on secondary embryoids of Brassica napus ssp. oleifera (Metzg.) Sinsk., winter oilseed rape, are reported. A kill curve was established, and the secondary embryoids were found to be more tolerant of high doses of irradiation than tissues of many other plant species. Secondary embryoids which had received less than 320 Gy retained their secondary embryogenic potential at subsequent subcultures, although their potential to develop into plantlets was greatly reduced. A haploid line from the cultivar Rapora was found to be more sensitive to gamma irradiation than a diploid line from the cultivar Primor. A number of regenerant plants have been established from irradiated embryoids and grown on to flowering.